The present invention relates to an ultrasonic diagnostic apparatus for providing a tomographic image of a region of interest of a subject or an object under measurement by utilizing ultrasonic waves and more particularly to an ultrasonic diagnostic apparatus in which transmission and reception of ultrasonic waves can be effected by means of a probe of multi channel and switching between the single beam reception and the simultaneous parallel beam reception can be ensured to perform signal processings.
As shown in FIG. 1, a conventional ultrasonic diagnostic apparatus comprises a probe 1 for transmitting and receiving ultrasonic waves to and from a subject, an ultrasonic signal transmitting and receiving unit 2 for amplifying receiving signals from the probe 1 and providing them with predetermined delays so as to perform receiving beam forming, an image processing circuit 3 for applying predetermined processings to output signals from the ultrasonic signal transmitting and receiving unit 2 so as to prepare an image signal, and an image display unit 4 for displaying the image signal from the image processing circuit 3. The ultrasonic signal transmitting and receiving unit 2 includes a transmitting circuit 5 for generating ultrasonic transmitting signals and applying them to the probe 1 to drive the same, a receiving and amplifying circuit 6 for receiving and amplifying reflected echo signals returning from the living body and received by the probe 1, and a receiving beam forming circuit 8 having a delay circuit 7 which provides receiving signals of respective channels delivered out of the receiving and amplifying circuit 6 with predetermined delays and adds the respective channel signals together to bring the channel signals into in-phase so as to accomplish receiving focusing.
Then, output signals from the receiving beam forming circuit 8 are put together to form a single channel signal, this signal is sent to the image processing circuit 3 so as to be subjected to signal processings such as logarithmic compression and detection and an image signal thus obtained is applied to the image display unit 4, thereby displaying an ultrasonic tomographic image. The apparatus of the above circuit construction is called a single beam reception type apparatus, in which through one transmission of ultrasonic beams from the probe 1 effected in a scanning direction for the one transmission in a sector scanning image shown in FIG. 2, one receiving signal is obtained and so only one scanning line is allowed to be obtained.
There is on the other hand another conventional example of ultrasonic diagnostic apparatus as shown in FIG. 3 wherein in a receiving beam forming circuit 8 of an ultrasonic signal transmitting and receiving unit 2, two delay circuits 7a and 7b are connected in parallel and succeeding two image processing circuits 3a and 3b are also connected in parallel. The apparatus of the above construction is called a simultaneous parallel beam receiving type apparatus, in which through one transmission of ultrasonic beams from probe 1 effected in a scanning direction for the one transmission in a sector scanning image shown in FIG. 4, two receiving signals are obtained and so two scanning lines returning from portions which are oppositely displaced from each other by a small angle are allowed to be obtained.
Under the condition described as above, the number of channels is related to the single beam reception type apparatus shown in FIG. 1 and the simultaneous parallel beam reception type apparatus shown in FIG. 3 as follows.
More particularly, in the observation of hearts in which the simultaneous parallel beam reception is the most effective, a probe must be applied between ribs and therefore the size of the probe in use cannot be large and the number of channels cannot be increased. On the other hand, since in the observation of the other organs than the heart a high frame rate as in the case of the heart observation is not required, the single beam reception is enough for practical use and improvements in acoustic characteristics are rather of importance. Therefore, in this case, there needs the multi channel. Recently, it is general to improve acoustic characteristics by increasing the number of channels used in one transmission/reception. Taking sector probes, for instance, a probe of 64 channels is generally used in the heart observation and a probe of the double of channels, that is, 128 channels is used in the observation of bellies devoid of obstructive bones.
With the trend toward the multi channel scheme as above, when a probe 1 of, for example, 128 channels is used in the single beam reception type apparatus shown in FIG. 1, receiving and amplifying circuit 6 and delay circuit 7 each being of 128 channels are necessarily used at the expense of increased cost and increased size in expectation of improvements in acoustic characteristics. However, in the simultaneous parallel beam reception type apparatus shown in FIG. 3, for the probe 1 of 128 channels, a single receiving and amplifying circuit 6 of 128 channels suffices but two delay circuits 7a and 7b each being of 128 channels are required. In this case, the delay circuits 7a and 7b of increased channels of 128 lead to an increase in size and cost and besides the number of channels of the two amounts up to 256 in total, with the result that the size of the apparatus as a whole is increased and the cost thereof is increased significantly.
Since the performance of the delay circuits 7a and 7b dominate the image quality, in other words, the performance of the ultrasonic diagnostic apparatus, high performance is required of the delay circuits. Accordingly, the delay circuit becomes very expensive and an increase in the number of channels of the delay circuit is of a significant problem from the standpoint of cost reduction.